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Improve heuristics check to detect broken RM2000-based fonts #3463

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Improve heuristics check to detect broken RM2000-based fonts #3463

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7ff7b87
Added a small heuristic check to font.cpp to identify broken fonts ba…
florianessl Aug 2, 2025
08223c3
Change the iterator variable type because the compiler complained abo…
florianessl Aug 2, 2025
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27 changes: 27 additions & 0 deletions src/font.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -33,6 +33,7 @@
# include FT_BITMAP_H
# include FT_MODULE_H
# include FT_TRUETYPE_TABLES_H
# include FT_FONT_FORMATS_H
#endif

#ifdef HAVE_HARFBUZZ
Expand Down Expand Up @@ -311,6 +312,32 @@ FTFont::FTFont(Filesystem_Stream::InputStream is, int size, bool bold, bool ital
if (!strcmp(face->family_name, "RM2000") || !strcmp(face->family_name, "RMG2000")) {
// Workaround for bad kerning in RM2000 and RMG2000 fonts
rm2000_workaround = true;
} else if (!FT_HAS_COLOR(face) && FT_HAS_FIXED_SIZES(face)) {
auto font_format = FT_Get_Font_Format(face);
if (!strcmp(font_format, "Windows FNT")) {
static constexpr std::array<std::pair<char32_t, int>, 4> glyphs = {{
{ 'h', 6},
{ 'l', 4},
{ 'I', 15},
{ ' ', 15}
}};
// Check some metrics to identify custom fonts which were based
// on the broken RM2000 font & thus also need the same workaround
rm2000_workaround = true;
for (size_t i = 0; i < glyphs.size(); ++i) {
auto glyph_index = FT_Get_Char_Index(face, std::get<0>(glyphs[i]));

if (glyph_index == 0 || FT_Load_Glyph(face, glyph_index, FT_LOAD_MONOCHROME | FT_LOAD_TARGET_MONO) != FT_Err_Ok) {
rm2000_workaround = false;
break;
}
auto advance_x = Utils::RoundTo<int>(face->glyph->advance.x / 64.0);
if (advance_x != std::get<1>(glyphs[i])) {
rm2000_workaround = false;
break;
}
}
}
}
}

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